This invention pertains to locked pipe joints, and especially concerns a packing for telescopic locked joints in which the end of a male pipe penetrates inside the end socket of a female pipe through the radial compression of the packing.
When a packed pipe joint has been made, the axial motion of the pipes in relation to each other must be prevented as they weaken the proper sealing of the joint, or may even disengage the initially joined pipes completely. This problem becomes especially acute when the pipes transport fluids under pressure. Indeed, the pressure of the fluid produces substantial forces, at each change in direction, which would tend to disengage the constituent elements of the joint.
Devices are known wherein the duct elements are arranged to thrust against foundations anchored in the ground. The major disadvantage of such devices is that they are very expensive, and they cannot always be installed.
Locking devices have also been proposed wherein annexed mechanical parts such as flanges are used to attach the tubular elements to be joined. Those devices are difficult to lay because they require the use of several mechanical parts with bolts, of which the implementation on site is quite delicate.
Moreover, one usually needs to alter the socket and the male end of the pipes to be joined by providing a ring-like groove on the male end, which tends to weaken the mechanical resistance of the joint.
Packed joints are also known in which locking elements located in the front part of the packing are inserted in a regular distribution at the open end of the socket. In such packings, as disclosed in French Pat. No. 2,186,621, the locking elements are fitted with several teeth, and are able to turn against an internal surface of the socket.
Experience has shown, however, that such packings display several problems when in use. First of all, the metal inserts, in the event of an optimal diameter for the male end, repel the sealing body from the packing in such a way that the seal is never completely guaranteed. Secondly, the range of diametric tolerance that is admitted by such a locking system is narrow, and in particular, it is lower than the range of tolerance in the manufacturing of pipes which requires the sorting of the pipes. Finally, where there is a withdrawal motion from the male end outside of the socket, the pivoting of the inserts is restricted by the nose of the socket. This means that the inserts will no longer hook the outer surface of the male end, rather they will rub against the male end, the locking system no longer being guaranteed as a result.